The present invention relates to a riser pipe element comprising at least one pipe or auxiliary line integrated in the central tube. The present invention proposes a specific element insofar as the auxiliary line or lines are connected to the central tube of an element of the riser so that they take up the mechanical stresses, notably longitudinal, together with the central main tube.
A drilling riser pipe consists of a set of tubular elements whose length ranges between 15 and 25 m (50 and 80 feet), assembled by connectors. The weight of these risers can be very great, which imposes suspension means of very high capacity at the surface and suitable dimensions for the central tube and the couplings.
Until now, auxiliary lines: kill lines, choke lines, are arranged around the central tube and comprise couplings that fit into one another, fastened to the connectors of the riser elements so that these high-pressure lines can allow a longitudinal play between two successive line elements, without disconnection however. It is not envisaged that these lines intended to allow high-pressure circulation of an effluent coming from a well or from the surface take part in the mechanical strength of the structure consisting of the riser pipe as a whole.
When drilling at water depths that can reach 3000 m, the dead weight of the auxiliary lines becomes very disadvantageous insofar as, for the same maximum operating pressure, the length of these lines imposes a greater inside diameter considering the necessity to limit pressure drops.
Modern calculation means have allowed to show the advantage afforded by making the auxiliary lines, kill lines, choke lines or booster lines, take part in the longitudinal mechanical strength of each riser element.
The present invention thus relates to a riser element comprising a main tube, connection means at both ends, at least one auxiliary pipe length arranged substantially parallel to said tube. The auxiliary pipe length is secured at both ends to the connection means of the main tube so that the longitudinal mechanical stresses to which the connection means are subjected are distributed in the tube and in the pipe.
One end of the auxiliary pipe can comprise a fastening device allowing a determined longitudinal play.
The play may not be zero in the absence of load on the element.
The auxiliary pipe can have one end running through a flange secured to a connector of the tube and it can comprise a dog limiting the displacement of said pipe in relation to the flange.
The play can correspond to the elongation of the main tube under a determined load value. The auxiliary pipe can be a steel tube hooped by reinforcing wire layers.
The main tube can be a steel tube hooped by reinforcing wire layers.
The reinforcing wires can be made of glass, carbon or aramid fibers coated in a polymer matrix.